Cytokines are immunomodulatory proteins that mediate immune system activation and responses, such as cell-mediated immunity and allergic type humoral responses. T lymphocytes (T cells), which are a major source of cytokines, possess antigen-specific receptors (the T cell receptor) on their cell surface, which allows recognition of foreign antigens. There are two main subsets of T lymphocytes, these being distinguished by the presence of cell surface markers known as CD4 and CD8. T lymphocytes expressing CD4 are also known as helper T cells, and these are regarded as being the most prolific cytokine producers. This subset can be further subdivided into Th1 cells and Th2/T17 cells, and the cytokines they produce are known as Th1-type cytokines and Th2/Th17-type cytokines respectively.
Th1 cells are characterized by the production of pro-inflammatory cytokines such as IFN-γ, IL-2, and TNF-β. Th1 cells are involved in cell-mediated immunity (CMI), this being the immune response typically mounted against viruses and intracellular pathogens. The cell-mediated response also eliminates cancerous cells and stimulates delayed-type hypersensitivity (DTH) skin reactions.
Th2 cells are characterized by the production of Interleukin-4 (IL-4), Interleukin-5 (IL-5), Interleukin-9 (IL-9), Interleukin-10 (IL-10) and Interleukin-13 (IL-13). Th2 cells are thought to play a role in allergy responses. Cytokines such as IL-4 generally stimulate the production of antibodies (the so called “humoral immune response”) directed towards extracellular organisms, such as parasites. IL-5 stimulates eosinophil responses, also part of the immune response toward large extracellular parasites.
Th17 cells secrete IL-17 and are involved in immune regulation in cancer and allergic reactions. Functionally, Th17 cells play a role in host defence against extracellular pathogens by mediating the recruitment of neutrophils and macrophages to infected tissues. They are, therefore, largely part of the humoral response together with Th2 cells. Identification of the Th17 family of effector T cells represented a major recent breakthrough. The IL-17 cytokine family is a group of cytokines including IL-17A, B, C, D, IL-17E (IL-25) and IL-17F. It is increasingly recognized that besides T cells, other cells such as NK cells and neutrophils might also be an important source of IL-17. Besides IL-17A, the major cytokine produced by Th17 cells, these cells also release IL-17F, IL-21 and IL-22.
It is hypothesised that in certain circumstances, the Th1 response or the Th2/Th17 response can cause disease. An over-reactive Th1 response can generate organ-specific autoimmune disease such as arthritis, multiple sclerosis, or Type I diabetes, while an over-reactive Th2/Th17 response may underlie allergy and atrophy. It is currently believed that Th17 cells play a major role in host defence against pathogens and an exaggerated Th17 response may lead to severe inflammatory responses and autoimmune diseases—inflammatory bowel diseases (IBD), namely, ulcerative colitis (UC) and Crohn's disease (CD), are chronic inflammatory processes of the gastrointestinal tract. In these diseases a disturbed and exaggerated immune response, mainly towards the endogenous microflora, plays a major role. IL-17 expression is increased in both UC and CD. Type I IFNs have been studied in clinical trials in patients with UC and demonstrated efficacy in selected studies. As anti-viral cytokines, it is now known that Type I IFNs can regulate the development of Th17 cells.
Either a Th1 response or a Th2/Th17 response can down-regulate the other and this is the basis for the so-called “Th1/Th2” hypothesis whereby an immune response may be skewed down either the Th1 or Th2/Th17 route, this being driven by the cytokine profile secreted by one cell group which may promote expansion of that cell type and restrict expansion of the opposing cell type.
Interferons (IFNs) are a family of proteins which are pleiotropic effectors of the immune system. Interferons may be classified into three distinct types—Type I interferons, Type II interferons and Type III interferons. Type I IFNs represent a family of highly homologous cytokines that have been found to activate a range of physiological responses, including anti-viral and anti-proliferative activities as well as playing an important role as activator of the immune response.
Type I interferons consist of interferon alpha (IFN-α), interferon beta (IFN-(β), interferon kappa (IFN-κ), interferon tau (IFN-τ), interferon nu (IFN-ν) and interferon omega (IFN-ω)). IFN-α is represented in the genome by 13 genes (12 subtypes), some of which have allelic variants and the different IFN-α gene products are called subtypes. All interferon subtypes consist of 166 amino acids stabilised by two disulfide bonds, except for IFN-α2 which has one amino acid less. The homology to mouse IFN-α is 40%.
There are 2 forms of IFN-α: (i) recombinant IFN-alphas which are designated IFN-α2a and IFN-α2b, with only one amino acid difference (IFN-α2a was cloned from a tumour cell line and occurs as a polymorphic variant in human populations); and (ii) a multi-subtype IFN-α, sometimes called natural IFN-alpha, which is expressed from the leukocyte fraction of human blood challenged with Sendai virus or produced by cell lines e.g. lymphoblastoid. This product is highly purified with a final immunoaffinity step and contains six major subtypes, namely, IFN-α1, IFN-α2, IFN-α8, IFN-α10, IFN-α14, and IFN-α21, the first two being the major components.
It is known that different pathogens induce different IFN-α subtypes in vitro and that IFN-α subtypes have different antiviral activities. Infection via a variety of routes, including orally, has been shown to induce different subtype profiles. IFN-α subtypes bind to the same receptor, activate common signaling pathways and are expected to have the same biological functions. Similar to many cytokines, two of the natural IFN-α subtypes are glycosylated. IFN-α14 has N-linked glycosylation, while IFN-α2 has O-linked glycosylation. Glycosylation influences the structure and the polarisation of the molecule, but no effects have been demonstrated on receptor binding or direct physiological function. Nevertheless, glycosylation could modulate recognition by the immune system or increase the half-life in the circulation.
All IFN-α subtypes have anti-viral activities, by definition, although their absolute efficacy in this context may vary considerably. In addition, many other biological properties have been described, but with varying potencies, including immunomodulatory and anti-proliferative activities. The pleiotropic effects appear to be due to differential interaction with the receptor chains and signaling through different intracellular pathways to an array of effector molecules.
Overall, IFN-α is part of innate immunity with strong links into adaptive immunity. Both T and B-cells are activated. IFN-α promotes the induction of a Th1 immune response, one mechanism being possibly through the enhancement of IFN-α-inducible protein-10 (IP-10) expression in dendritic cells. Few studies deal with the role of subtypes in T helper-regulation while the cytolytic activity of both T-cells and NK-cells is enhanced.
IFN-α may have a key role in the regulation of the Th1 response. It has been shown that IFN-α treatment promotes Th1 cell differentiation indirectly (largely via IFN-γ), but also appears to suppress Th2 cell development through the suppression of IL-4 and IL-13 gene expression. IFN-α therefore is able to re-establish a Th1/Th2 population balance in diseases and infections that promote a Th2 cell imbalance. In recent years, it became evident that besides its anti-viral effects, several immunomodulatory functions are exerted by IFN-α. IFN-α can impact on dendritic cell differentiation and controls the expression of various pro-inflammatory cytokines such as IL-8 or IL-18 and induces several anti-inflammatory mediators such as IL-1 receptor antagonist (IL-1Ra), soluble TNF receptor p55, IL-10 and IL-18 binding protein. However, the mechanisms of actions of IFN-α are still only partly understood.
In patients with allergy or allergic disease, a Th2-predominant immune response is generated. Th2 cells secrete IL-4 and IL-13 driving B cells to produce Immunoglobulin E (IgE) antibodies specific to an allergen. An allergen is an antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals mainly through Immunoglobulin E (IgE)-mediated responses. Following that, IgE binds to its high affinity receptor on mast cells, skin cells and mucosal tissues. Upon exposure to the allergen, mast cells release their contents, which include histamine, leukotrienes and prostaglandins. This causes allergic symptoms including, but not limited to, red eyes, itchiness, runny nose, eczema, urticaria, angioedema, shortness of breath, wheezing, coughing, an asthma attack, abdominal pain, vomiting, diarrhoea or even anaphylaxis.
Allergic diseases are among the most common form of chronic illness. The World Health Organisation estimates that over 20 percent of the world population is affected and Europe alone has over 80 million sufferers (Global Allergy and Asthma European Network, 2008). An allergic reaction is usually caused by hypersensitivity of the immune system to an allergen, causing a misdirected immune response. Mild allergies, such as hay fever, are very common in the human population. Severe allergies can be caused by dietary allergens, such as food, by environmental allergens, such as the venom of stinging insects, by medication or can be genetically determined.
Food allergy is a major health concern, which is estimated to affect around 6% of young children and 3-4% of adults in Western societies. Food allergy is hypothesised to result from a breakdown in oral tolerance to ingested antigens or allergens. Food allergies and associated allergic diseases include, but are not limited to, dairy (milk) allergy, including Heiner syndrome, egg allergy, soya allergy, fish (shellfish) allergy, peanut and tree nut allergy, sesame and other seed allergy, gluten (wheat) and grains allergy, fruit and vegetable allergy, caffeine allergy, oral allergy syndrome, alcohol allergy, pollen food allergy syndrome, eosinophilic gastroenteritis, IgE mediated gastrointestinal food allergy and C1 esterase deficiency.
Management and treatment of allergic disease is usually via three general approaches: (i) avoidance of the allergen; (ii) medications that target disease symptoms and (iii) conventional immunotherapy, known as desensitisation, which aims to enhance the Th1 response in established disease. However, these approaches are far from ideal. Avoidance of allergens is not always possible, medications that target disease symptoms, such as anti-histamines, provide only short-term relief and desensitisation involves the use of the actual allergen, which can result in potentially frequent harmful side-effects. The possibility of anaphylaxis is never completely eliminated in patients suffering from allergic diseases and this causes a great deal of stress to the patient and their families.
The present inventor submits that it would be desirable to develop an immunotherapeutic approach which involves safer use of an allergen, as lower doses may be employed, and provides longer-term protection against the allergic reaction. Since allergy results from over-reactivity of Th2/Th17 cells and a corresponding lack of activity of the Th1 response, a medication that is able to modify and balance a misdirected Th2/Th17 response would be beneficial in preventing the allergic reaction. Such a medication would further be suitable to treat diseases and conditions where an exaggerated Th17 response plays a role, such as IBD. Additionally, the inventors consider the ability to enhance of a Th1-mediated immune response and suppress a Th2/Th17-mediated immune response would be useful in the provision of compositions that mediate immune response in subjects with cancer.